The Amazon River basin is brimming with colorful and exotic creatures, all with unique characteristics. Take, for example, the sloth: Sleeping up to 20 hours a day, the world's slowest mammal actually sports a coat of algae on its fur, which provides camouflage for the lethargic tree-dweller. The skin of the poison dart frog, marked by bright colorful stripes, secretes a toxin strong enough to paralyze or even kill predators. Other fascinating species make their home in this forested region, and river cruises offer a way to get up-close looks at many of them.

You may not spot a howler monkey on your trip, but there's a good chance you'll hear one. These primates have a distinctive warning call that can be heard up to 2 miles away. Other sounds you might hear in the jungle include the whistles and chatter of the vibrant scarlet macaw or the roar of the elegant jaguar, the third-largest cat in the world.

The uncommon species are not limited to mammals and birds. Palms, vines, bromeliads, orchids, giant lilies and carnivorous plants are on the extensive list of flora found here.

And the river itself teems with life. One rare river dweller is the Amazon dolphin, or boto, which has a more elongated beak than the ocean dolphin; this helps it root for food in the muddy waters. While the females are usually gray, the male botos are a distinct pink color. Folktales claim the dolphins are enchanted shape-shifters who sometimes take human form to lure men and women to a mythical underwater city.

Also in these legendary waters are sharp-toothed piranhas, giant river otters, green anacondas -- the largest snake in the world -- and nocturnal caimans.